APM and ASM memory usage for sizing a box

I actually have a related question rather than an answer to yours. Is it normal and expected that actual memory usage by ASM will steadily increase as ASM is enabled for more VS's? I have a somewhat unique environment in that I have a large number of VS's, each for unique customers, but the same web application behind each (well, same webapp code in front of unique customer databases). So while I have only one policy I have hundred's of VS's that I am/will be applying this policy to. Do you know John if there is any known formula for calculating total ASM memory usage based on the number of VS' for which it is deployed? Thank you.